Research Proposal: Babesia bovis is one of the most significant parasites of cattle worldwide. Morbidity and mortality associated with babesiosis and other important apicomplexan diseases, such as malaria, coccidiosis and theileriosis, has prompted intensive efforts to improve currently inadequate control methods. Possible novel targets for control are the apical complex organelles that are unique to the Apicomplexa and perform important, although incompletely understood, functions in their life cycles. Ultrastructural evidence strongly implicates the involvement of the apical complex in host cell invasion. In addition, antibody to several apical complex proteins can block erythrocyte invasion. This has yet to be demonstrated for B. bovis. In the proposed studies, 1) apical complex organelles will be isolated, and 2) polyclonal and monoclonal antibody reagents to apical complex organelles and proteins generated, respectively. These reagents will be used in future experiments to test the hypothesis that antibody to apical complex proteins will inhibit erythrocyte invasion by B. bovis merozoites. This strategy is designed to rapidly identify apical complex proteins which function in invasion. Once identified, the molecular details of their roles in the invasion process can be investigated in long-term studies. Candidate: The candidate is a veterinarian completing the clinical service component of a residency in veterinary anatomic pathology, and is a candidate for the Ph.D. in veterinary science . The experiments described in this proposal will constitute Specific Aims 1 and 2 of her doctoral research. The results will provide directions for the long-term objective of elucidating the mechanisms of host cell entry by apicomplexan parasites. Environment: The Department of Veterinary Microbiology and Pathology is recognized for contributions to the molecular biology and immunology of veterinary infectious diseases, and has facilities equipped for performing technologically current research in these areas. Collaborative research in bovine babesiosis figures prominently among departmental projects. The primary sponsor has experience in the molecular biology of protozoan and metazoan parasites, including intracellular parasite development, and isolation and characterization of immunoprotective surface proteins.